With the rising costs and environmental concerns associated with fossil fuels, renewable energy sources have become increasingly important. The development of renewable fuel sources provides a means for reducing the dependence on fossil fuels. Accordingly, many different areas of renewable fuel research are currently being explored and developed.
With its low cost and wide availability, biomass has increasingly been emphasized as an ideal feedstock in renewable fuel research. Consequently, many different conversion processes have been developed that use biomass as a feedstock to produce useful biofuels and/or specialty chemicals. Existing biomass conversion processes include, for example, combustion, gasification, slow pyrolysis, fast pyrolysis, liquefaction, and enzymatic conversion. One of the useful products that may be derived from the aforementioned biomass conversion processes is a liquid product commonly referred to as “bio-oil.” Bio-oil may be processed into hydrocarbon chemicals, specialty chemicals, and/or other useful products, e.g., bio-fuel, such as, transportation fuels and heating oil.
Despite recent advancements in biomass conversion processes, many of the existing biomass conversion processes produce low-quality bio-oils containing high amounts of oxygen, which are difficult, if not impossible, to separate into various fractions. These bio-oils require extensive secondary upgrading in order to be utilized as heating oils or heating fuels due to the high amounts of oxygen present in the bio-oil.
More specifically, the production of bio-oil by pyrolysis, both fast and slow, can be problematic. Pyrolysis is characterized by the thermal decomposition of materials in an oxygen-poor or oxygen-free atmosphere (i.e., significantly less oxygen than required for complete combustion). In the past, pyrolysis has referred to slow pyrolysis whose equilibrium products included non-reactive solids (char and ash), liquids (tar and/or pyroligneous liquor), and non-condensable gases.
More recently, it has been recognized that pyrolysis can be carried out through a fast (rapid or flash) pyrolysis method where finely divided feedstock is rapidly heated and the reaction time is kept short, i.e. on the order of seconds. Such fast pyrolysis results in high yields of primary, non-equilibrium liquids and gases (including valuable chemicals, chemical intermediates, hydrocarbon chemicals and bio-fuels).
The non-equilibrium liquids (or bio-oil) produced by fast pyrolysis are suitable as a fuel for clean, controlled combustion in boilers and for use in diesel and stationary turbines. In fact, such bio-oil liquids offer some distinctive advantages for heating and power production over biomass gasification products and direct combustion of the biomass. Some of the advantages of bio-oil are:                Higher energy densities compared to direct combustion of the raw biomass;        More easily/cost effective to transport and handle than raw biomass or producer gas;        Existing boilers may be used with bio-oil, subject only to retrofitting;        Fewer emissions in boiler use compared to solid fuels due to better control of the combustion process; and        Bio-oil from pyrolysis processes is the least cost liquid bio-fuel for stationary use and its net CO2-balance is better than that of other bio-fuels.        
However, besides all those advantages, instability, corrosiveness and low heating value compared to conventional heating oil, have precluded a full success of pyrolysis bio-oils as a heating fuel. Moreover, it has been recognized that pyrolysis derived bio-oils are unsuitable for use as a heating oils and cannot be directly used as a heating oil without subsequent hydrotreating (see for example EP 0718392 and WO 2009/126508). In fact EP 0718392 notes that hydrotreating to completely remove oxygen from bio-oil would represent a major and prohibitive cost because of the high oxygen content of pyrolysis derived bio-oil. Further, in order for bio-oil to be used in certain fuel-powered devices, e.g., devices that utilize petroleum-based fuel, the device and its ancillary equipment may require a broad range of modifications. For example, in certain boilers or other fuel-powered devices, one may need to modify the ignition system in order to use a bio-oil in such a device.
Accordingly, it would be advantageous to develop a pyrolysis derived bio-oil that could be used as a bio-fuel, e.g., heating oil, wherein such bio-fuel has improved stability, less corrosiveness and higher heating value than prior art bio-oils without having to undergo hydrotreating or other deoxygenating processes. Further, there is a need for a bio-fuel that can be used in a fuel-powered device, e.g., a device designed for use with petroleum-based fuel, without having to modify such a device and its ancillary equipment.